A thermal standard noise

gas discharge noise generators and a calibrating radiometer for 4mm band are discussed. Advantages and weak points of both the total-power and Dicke radiometers are evaluated. A calibrating system of total-power radiometer with IF attenuator has been set up

and its equalization and error equations are derived and analysed in this paper. An advantage of this system is that it can be used in all frequency bands. Furthermore

it uses fewer waveguide components

and the microwave precision attenuator can be substituted by a precision IF attenuator. This is of practical significance for millimeter and submillimeter bands. This system

when used to calibrate gas discharge noise generators

gives an excess-noise ratio of 16.2 dB

the total error being ±0.45 dB. If the accuracy of the IF attenuator is 0.02 dB

the total crror will be ±0.3 dB.